The present invention concerns a device designed for controlling the operating pressure between two rotary cylinders in a machine used for processing layers such as webs, ink films, or the like.
An offset, flexographic, or rotogravure printing machine has at least a pair of rotary, or interacting cylinders (or rollers). The force tending to push these cylinders against one another is to be controlled accurately in the course of their processing a layer situated on their contact line (or surface). In the case of an offset printer, for example, the layer to be processed might be either a paper (or cardboard) web situated between the offset (or blanket) cylinder and the impression cylinder (or countercylinder), or else a thin ink film situated between the plate cylinder (or block cylinder) and the offset (or blanket) cylinder. Such cylinder pairs all have a common feature in that, in the course of a run, the two cylinders are to be pressed against one another so as to provide not only an operating pressure but also a pretension effect in such a way that even an interfering force of more than the operating pressure will not entail any difference of distance between axles. This pretension effect has been obtained up to now by means of running cables added to the radial periphery of both axial ends of the two cylinders.
However, such running cables have the following shortcomings:
an inherent seizing risk caused by inadequate lubrication due to lack of cleanness;
expensive cylinders;
the operating pressure can be modified only by changing the coating, unless the cables are put on eccentrics--which system, though, is complicated and expensive. At any rate, changing the operating pressure involves a machine stop, which is actually the main disadvantage.
Another negative feature existing on most of the arrangements of the prior art is the unchangeable distance between the PP-PB or PB-CC axles, which means that in the event of sudden overthickness, unfailing damage will occur on the blankets and the printing plate, or even of the bearings in particular cases.